Prediction and Experimental Validation of Burst Pressure of a Gimbal Bellow Used in a Cryogenic Stage of a Launch Vehicle

Gimbal bellows are used in the feed systems of the cryogenic stage of an indigenously developed launch vehicle for minimizing the actuator loads as well as convey the propellants to the cryogenic engine, whilst it is gimballed. Gimbal bellow is a universal joint in which two rotational degrees of freedom with specified stiffness are provided. As a part of design qualification of the bellow duct, structural capability of gimbal bellow with respect to pressure is required to be demonstrated through a burst test. Non-linear elastoplastic stress analysis is carried out for the estimation of burst pressure of the gimbal bellow. Burst pressure is estimated based on the pressure at which deformation shows an asymptotically increasing behaviour and the analysis un-converges. The instrumentation is designed for the measurement of displacements and strains at critical locations, and burst pressure test is conducted. The predicted burst pressure of gimbal bellow through simulation is 7.46 MPa compared to the tested burst pressure of 7.89 MPa. The burst pressure and the strain/displacement values matched very well with analysis predictions. The location of failure also matched favourably.